As is known in the art, phased array systems are used to collimate and direct a beam of wave energy, such as, for example electromagnetic energy, as in phased array antenna systems used in radar systems or in optical beam energy systems, or In acoustic energy systems as in ultrasound systems or sonar systems.
One such radar phased array antenna system includes a flat panel having rows and columns of antenna array elements and interspersed DC DC converters, as shown in FIG. 1, each array element having: an antenna, a transmitter and receiver coupled to the antenna element through a circulator or transmit/receive switch, and a phase shifter/attenuation section (i.e., Common Leg Circuit (CLC)) coupled to a radar system, as shown in FIG. 1A for an exemplary one of the array elements. The flat panel. is sometimes referred to as a Circuit Card Array, (CCA) comprised of a collection of Unit Cells (i.e., the above-described antenna element) that contains highly integrated electronic circuits, antennas and other microwave components, as shown in FIG. 1.
The radar system produces a transmit voltage between a VT BUS and a ground bus VGND for all of the array elements and a receive voltage between a VR BUS and the ground bus VGND for all of the arrays elements. The DC-DC converters are coupled to these busses as shown in FIG. 1A to provide, for each array element, a transmit voltage source VT and a receive voltage source VR, each relative to ground potential. It should be understood that the voltage VT BUS may be different from the voltage VT, and the that voltage VR BUS may be different from the voltage VR.
Within each element, the phase shifter/attenuation section provides the phase setting, amplifications and control functions to provide, with other elements in the array, the collimated and directed beam of radio frequency energy, The array element also includes a bias network responsive to a transmit/receive (T/R) control signal provided by the radar system. The function of the bias network is to provide “on” DC bias VPA (here indicated as the voltage VT) to an RF Power Amplifier (PA), here a Gall power amplifier, used in the transmit section of the array element during the transmit mode. In the absence of such bias, the transmitter is “off”, Likewise, the bias network provides “on” DC bias VRx (here indicated as the voltage VR) to a Low Noise Amplifier (LNA), here a GaAs limiter and LNA, in the receiver section of the array element during the receive mode. In the absence of such bias, the receiver is “off”, The bias network also provides DC bias voltage VCLC (here indicated as V) to amplifiers, variable attenuators, and phase shifter used in the phase shifter/attenuation section of the Common Leg Circuit,
More particularly, referring to FIG. 1B, the bias network includes a capacitor CT selectively coupled to either: (1) a transmit power source here the transmit voltage source VT provided by the DC-DC converter during a receive mode; or (2) the transmit section, as shown in FIG. 1C during the transmit mode. The bias network includes a pair of switches SA and SB operated by the transmit/receive (T/R) control signal provided by the radar system. Switch SA has a common terminal C and two pair of terminals L1, and L2; and L3 and L4. Switch, SB has a common terminal C and a single pair of terminals L1 and L2. The phase/amplitude control signals for the phase shifter/attenuator section are provided by a beam steering computer, not shown, within the radar system.
Referring now more particularly to FIG. 1C, during a receive mode (or during an initialization phase), switches SA and SB are positioned as shown, More particularly, the common C of switch SA is connected to L1 and to L4. The DC-DC converter produced voltage VT is therefore coupled to capacitor CT and decoupled from the transmitter to bias the transmitter “off”. Therefore, the capacitor CT is charged by the DC-DC converter voltage VT by a charging path indicated by the arrow. The common C of switch SB is connected to L1 and decoupled from terminal L2 thereof so that the receiver is biased “on” by a second DC-DC converter voltage VR.
During the transmit mode, as shown in FIG. 1C, switches SA and SB are positioned as shown. More particularly, the common C of switch SA is connected to L2 and L3 and therefore the DC-DC converter voltage VT is decoupled from the transmitter and the transmitter is biased “on” by the charge stored on the capacitor CT. The common terminal C of switch SB is coupled to terminal L2 and decoupled from terminal L1 thereby removing the DC-DC converter voltage VR from the receiver to thereby bias the receiver “off”.
The inventor has recognized that power provided by the DC bias source also has accompanying unwanted noise from various sources. The bias network itself is typically a Single Pole Double Throw switch. During the receive portion of the periodic transmit/receive Radar Cycle, the capacitor CT is charged from a voltage source VT. This capacitor is located close to the PA and is large enough to provide all the energy needed for the transmit pulse. The proximity of the capacitor to the PA insures that the pulse shape is sharp and does not suffer from the inductance and resistance of the radar system power busses under high current conditions. Because of the transmit duty cycle, the discharge versus charge current ratio can be as high as 10 to 1. In the systems described above in connection with FIGS. 1A, 1B and 1C, an important function of the capacitor CT is to allow disconnect of the transmitter from the radar system power busses and thereby prevent bus noise from corrupting the transmit signal. Indeed, during transmit, bias power is provided only from the proximal capacitor, CT. On the other hand, the inventor has recognized that in the system described above in connection with FIGS. 1A, 18 and 1C, the receive bias, V, is provided by a separate, potentially noisy, power bus connected to the bias network typically at a lower voltage than that for transmit. There is a separate bias switch shown in FIGS. 1B and 1C synchronized to disconnect the receiver when the transmitter is on. The array element must be biased during both the transmit mode and receive mode. The bias power required by the receiver is small compared with that needed by the transmitter. Accordingly, the receive power is provided directly from the radar system low voltage power bus without providing a local storage capacitor. However, the inventor has recognized that with this configuration, bus noise can be impressed not only on CLC but also on the receiver. These noise sources degrade system signal to noise ratio. The system of the present disclosure introduces a capacitor that provides stored energy to power the CLC and receive functions within the antenna element.
In accordance with the present disclosure, an antenna element, comprises: a transmitter; a receiver; a transmit supply capacitor; a receiver capacitor; a transmit power source; a receive power source; and bias network circuitry for: during a receive mode, charging the transmit supply capacitor from the transmit power source while decoupling the receive supply capacitor from the receiver power source and coupling the receive supply capacitor to discharge and thereby provide bias to the receiver; and during a transmit mode, charging the receive supply capacitor from the receive power source while decoupling the transmit supply capacitor from the transmit supply capacitor and coupling the transmit supply capacitor to discharge and thereby provide bias the transmitter.
Disconnecting the array elements in the array from a common source of power allows for element-by-element noise de-correlation thereby improving noise performance for the array. Because of the phasing of the switch states, the receiver bias capacitor is charged and discharged inversely to charging and discharging of the transmit supply capacitor. Providing local energy storage to all the circuit components will improve the shaping of the bias pulses.
In one embodiment, the antenna element includes a phase shifter/attenuator section having an amplifier and a phase shifter and wherein bias voltage is provided to the amplifier and phase shifter by the transmit supply capacitor during the transmit mode and the receive supply capacitor during the receive mode.
The details of one or more embodiments of the disclosure are set forth in the accompanying drawings and the description below. Other features, objects, and advantages of the disclosure will be apparent from the description and drawings, and from the claims,